Die and punch sets

ABSTRACT

A die and punch set suitable for extruding metals such as steel the die and punch set including a hollow die and a punch intended to enter the die to extrude metal from material received within the die and characterised in that the die and/or the punch is formed of hot pressed silicon nitride.

United States Patent [191 Lawson [451 Apr. 30, 1974 1 DIE AND PUNCH SETS [75] Inventor: Ralph Leonard Joseph Lawson,

Selly Oak, Birmingham. England [73] Assignee: Joseph Lucas Industries Limited,

Birmingham, England 221 Filed: Apr. 24, 1972 21 1 Appl. No.: 246,548

[30] Foreign Application Priority Data Apr. 27, 1971 Great Britain 11509/71 [52] [1.5. CI 72/267, 72/467, 76/107 R [51 Int. Cl. B216 25/02 [58] Field Of Search 72/467, 354, 359, 267,

[56] References Cited UNITED STATES PATENTS 2,882,759 4/1959 Altwicker 76/107 A 2,618,565 11/1952 Nicholson.... 423/344 2,636,828 4/1953 Nicholson 423/344 Primary Examiner-Richard J. Herbst Attorney, Agent, or FirmHo1man & Stern [5 7] ABSTRACT A die and punch set suitable for extruding metals such as steel the die and punch set including a hollow die and a punch intended to enter the die to extrude metal from material received within the die and characterised in that the die and/or the punch is formed of hot pressed silicon nitride,

3 Claims, 3 Drawing Figures mimimraao 1924 v 3; 807.212

FIG. 3.

1 DIE AND PUNCH SETS This invention relates to die and punch sets suitable for extruding metals, such as steel, and of the kind including a hollow die and a punch intended to enter the die to extrude metal from material received within the die.

In known die and punch sets suitable for extruding metals, the die and the punch are formed of steel or tungsten carbide. However, a disadvantage exists with these known sets in that before a metal component can successfully be extruded the component must undergo an involved, and therefore lengthly lubricationtreatment. The conventional lubrication treatment in the case of a steel component includes removal of grease from the component followed by an acid pickling process, which prepares the component for a subsequent phosphating and soaping treatment. In particular, the phosphating treatment is required so that a parting layer is produced between the component and the extrusion tools since without the phosphating localised welding between the tools and the component can result. The soaping treatment lowers the friction between the component and the extrusion tools during movement of the punch into the die, whereby the punch load required to effect the extrusion and hence the stresses within the extrusion tools are reduced. It has now been found that if the die and/or the punch are formed of hot-pressed silicon nitride, then the use of the lubrication treatment described above, prior to extrusion, can

be avoided or, alternatively a greatly. simplified lubrication treatment can beused.

Accordingly, in one aspect the invention resides in a die and punch set of the kind specified wherein the die and/or the punch is formed of hot-pressed silicon nitride.

Preferably, where the extrusion process is arranged so that metal from said material flows, during extrusion, in the same direction as the direction of movement, of the punch, at least the die is formed of silicon nitride.

Alternatively where the extrusion process is arranged so that during extrusion metal flows in the opposite direction to the direction of movement of the punch, at least the punch is formed of silicon nitride.

Preferably, the punch forms part of a punch assembly and is removable from the remainder of the assembly so as to permit replacement of the punch.

In a further aspect, the invention resides in a method of extruding a metal using a die and punch set as described in the preceding paragraphs.

In the accompanying drawings,

FIG. 1 is a sectional view illustrating an extrusion process using adie and punch set according to a first example of the invention.

FIG. 2 is a sectional view illustrating anextrusion process using a die and punch set according to a second example of the invention, and

FIG. 3 is an exploded part sectional view of a punch assembly incorporating the punch shown in FIG. 2.

Referring to FIG. 1, in a first example of the invention a steel component 11 is produced by performing an impact extrusion operation on a bright drawn steel billet (not shown) using a first die and punch set 12. The die and punch set 12 includes a hollow die 13 formed of hot-pressed silicon nitride and a punch 14 formed of tungsten carbide. The hot-pressed silicon nitride die 13 is formed by heating silicon powder to'a temperature not exceeding 1,300 C in a non-oxidising atmosphere containing nitrogen", whereby the silicon powder is converted into silicon nitride which is substantially entirely in the a-phase. The silicon nitride powder is next intimately mixed with not more than I percent by weight of magnesium oxide by wet ball milling in butanol for a period of 72 hours. The mixed powder is then formed into the hollow die 13 by pressing the powder between graphite dies at a temperature not exceeding l,650 C and at a pressure of 4,000 lbs per square inch. In use, a conventional metal shrink ring is fitted around the die 13 so as to ensure that the silicon nitride of the die is under compression.

The arrangement of the die and punch set 12 is such that when the steel billet is inserted into the die 13 and the punch 14 is moved into the die to effect the impact extrusion process, metal from the billet flows in the direction of movement of the punch 14 to produce the component 11. Using the die and punch set 12 his found that the extrusion of metal from the billet can be successfully effected without the initial lubrication of the billet by conventional phosphating and soaping treatments. Further, as shown in the drawing, the die and punch set 12 includes an ejector punch 15 by means of which the extruded component 1 1 can be removed from the die. v

As shown in FIG. 1, the bore in thesilicon nitride die 13 used in the above example is stepped to define a wide portion and narrow portion, metal flowing into the narrow portion of the bore during the extrusion process to produce the component 11. In a modification of the above example, however, the die 13 is defined by an outer sleeve formed of tool steel, such as is used in conventional extrusion dies, and an annular insert formed of hot pressed silicon nitride which is positioned in the bore in the outer sleeve so that the bore in the assembled die 13 is stepped as shown in FIG. 1'.

Referring now to FIGS. 2 and 3, in a second example of the invention a second die and punch set 16 is used to effect a further impact extrusion process on the component 11, after the initial extrusion by the die and punch set 12. The die and punch set 16 includes a hotpressed silicon nitride punch 17, formed in a similar manner to that described for the die 13, and a die 18 formed of high speed steel type B.S.S. M2, the set 16 being arranged so that when the punch 17 is moved into the die 18 metal from the component ll flows in the opposite direction to the direction of movement of the punch 17. This type of extrusion process is known as a backward extrusion, as distinct from a forward extrusion where, as in the first example, metal is caused to flow in the direction of movement of the punch effecting the extrusion. Thus, to produce the required metal flow, the end 19 of the punch 17 which enters the die 18 to effect the backward extrusion is of conical form with an angle of being defined at the apex of the cone. Since the punch 17 is formed of hot-pressed silicon nitride, it is necessary to ensure, if the punch is to have a long working life, that the only forces acting on the punch in use arecompressive forces rather than tensile forces. Thus, the body of the punch 17 adjacent the end 19 is tapered with a very fine surface finish, that is in the region of between 2 and 5 micro inch for the average height of peaks on the surface, and without any additional shaping which is often incorporated in a backward extrusion punch to enhance metal flow. It

will .be appreciated that the body of the punch 17 is tapered in order to facilitate removal of the component from the punch after the operation without imposing on the punch tensile stresses in excess of that which the punch can accommodate In this particular example the body taper is in the order of a 7 included angle. The silicon nitride punch 17 is supported by a steel, punch carrier member 21 and defines with the carrier member 21 and a steel backing member 22 a punch assembly 23. The punch 17 is removable from the punch assembly 23 so that ready replacement of the punch 17 is possible. As in the previous example, when the die and punch set 16 is required to effect impact extrusion of the component 11, it is found that the extrusion process can be successfully effected without initial lubrication of the component by the standard phosphating and soaping treatments. Further, as in the example described above, in order to facilitate removal of the component after the extrusion'process, the die and punch set 16 includes an ejector punch 24.

It is to .be appreciated that in the first example the 4 formed of hot-pressed silicon nitride. Further, it is to be appreciated that although forming of the die and/or the punch of a die and punch set from silicon nitride avoids the requirement that the component to be extruded should initially undergo the complex lubrication treatment described above, lubrication can still advantageously be applied to the component but any such lubrication treatment only needs to be very simple.

1 claim:

l. A die and punch set of the kind specified wherein at least one of the die and punch is .formed of hotpressed silicon nitride, the arrangement being such that when the punch enters the die to effect extrusion, metal from the material being extruded flows in the opposite direction of movement of the punch, and wherein at least the punch is formed of silicon nitride.

2. A die and punch set as claimed in claim 1 wherein the body of the punch is tapered to facilitate removal of the component from punch after the extrusion oper- I 7 included angle. 

2. A die and punch set as claimed in claim 1 wherein the body of the punch is tapered to facilitate removal of the component from punch after the extrusion operation.
 3. A die and punch set as claimed in claim 2 wherein the taper of the body of the punch is of the order of a 7* included angle. 